The kinetic properties and substrate specificity of the various isozymic forms of rabbit liver glycogen branching enzyme, which have been isolated as pure proteins, will be studied in detail. The interaction of these isoenzymes with glycogen synthase to produce branched polysaccharides in vitro, will be studied by following their rate of synthesis from UDPG. The detailed molecular architecture of these products will be investigated by the use of several degradatory enzymes, and the results will be used to deduce information about substrate specificity and mode of action of the various branching enzyme isozymes which have been discovered. The metabolism of intra-lysosomal glycogen in human skin fibroblasts grown in tissue culture will be studied. The demonstrated possibility of using disaccharide inhibitors of lysosomal alpha-glucosidase to effect glycogen storage will be further studied to find whether or not such storage is exclusively lysosomal and to find, by isopycnic centrifugation, what enzymes such subcellular "storage" particles contain. This work bears on the general problem of lysosomal heterogeneity and relates to the metabolic role of the intralysosomal degradation of glycogen in normal human fibroblasts and the heritable block in this pathway which characterizes the infantile form of Type II glycogen storage disease.